Imaging system

ABSTRACT

An imaging member comprising a substrate, at least partially transparent to ultrasonic radiation, with a thin layer of liquid thereon, the layer preferably of a particular preferred thickness, is used for the detection of the interference pattern resulting from the interference of two phase correlated beams of ultrasonic energy, one beam typically being a reference beam and the other an object modulated beam. The free surface of the thin liquid layer is deformed by the interference pattern to form an acoustic hologram which may be used to reconstruct an optical image of the object and may be used in other advantageous ways as described herein. Electric field techniques to amplify the ultrasonically produced pattern of deformation of the free surface of the thin liquid layer; a diverging acoustic lens and a method of making a preferred elastomeric liquid layer are also described.

United States Patent [191 Sheridon June 26, 1973 IMAGING SYSTEM [75]inventor: Nicholas K. Sheridon, Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford, Conn.

[22] Filed: Jan. 12, 1972 21 Appl. No.: 217,164

Related US. Application Data [63] Continuation of Ser. No. 804,539,March 5, 1969,

abandoned.

52 US. ci 33075 n, 73/675 H, 350/35 [51] Int. Cl. G0ln 29/04 [58] Fieldof Search 340/5 H, 5 MP;

[56] References Cited UNITED STATES PATENTS 3,434,339 3/1969 Stetson etal. 340/5 H X 3,564,905 2/1971 Brenden et al. 340/5 H X PrimaryExaminerRichard A. Farley Attorney-James J. Ralabate, David C. Petre andGaetano D. Maccarone et a1.

[57] ABSTRACT An imaging member comprising a substrate, at leastpartially transparent to ultrasonic radiation, with a thin layer ofliquid thereon, the layer preferably of a particular preferredthickness, is used for the detection of the interference patternresulting from the interference of two phase correlated beams ofultrasonic energy, one

beam typically being a'refe'rence beam and the other an object modulatedbeam. The free surface of the thin liquid layer is deformed by theinterference pattern to form an acoustic hologram which may be used toreconstruct an optical image of the object and may be used in otheradvantageous ways as described herein. Electric field techniques toamplify the ultrasonically produced pattern of deformation of the freesurface of the thin liquid layer; a diverging acoustic lens and a methodof making a preferred elastomeric liquid layer are also described.

59 Claims, 8 Drawing Figures 1 IMAGING SYSTEM BACKGROUND OF THEINVENTION This application is a continuation application of priorcopending patent Ser. No. 804,539 filed Mar. 5, 1969 and now abandoned.

This invention relates to an imaging system and more specifically to anovel ultrasonic holography imaging system.

High frequency sound like coherent light can be used to construct ahologram. A background on optical holography is found in the BACKGROUNDsection of my copending application Ser. No. 728,986, filed May 14, 1968and now US. Pat. No. 3,580,657

Preston and Kreuzer, Applied Physics Letters, 10,

No. 5, 150 (Mar. 1, 1967) describes making ultrasonic holograms byscanning an ultrasonic receiver carefully along the interference patternof two ultrasonic beams and recording the instantaneous ultrasonicintensity as a photographic film density. The original object can thenbe reconstructed by illuminating the photographic film with light.Mueller and Sheridon, Applied Physics Letters, 9 No. 9,328 (Nov. 1,1966) describes making ultrasonic holograms by directing the referenceand object modulated ultrasonic beams toward the surface of a liquidmedium in which they are propagating. These beams, interfering at theliquid surface, give rise to a radiation pressure displacement of theliquid surface to form a stationary ripple pattern.- UsingSchlieren-like techniques the stationary ripple pattern was thenrecorded on photographic film. When the photographic film wasilluminated with coherent light, a reconstructed image, visible to thehuman eye, of the original object was obtained. Young and Wolfe, AppliedPhysics Letters, 11 No. 9,294 (Nov. 1, 1967) discloses recordingultrasonic holograms using deformable films on solid substrates.

While advantageous, in all of these schemes, the quality of the image ofthe reconstructed object suffered because in addition to the deformationpattern produced by the object beam interfering with the reference beam,the liquid or softened plastic material surface was also distorted byextraneous signals such as surface waves created by building vibrations,by objects moving in the liquid and by displacement of the liquidsurface due to acoustic streaming to cause over modulation of thedeforming surface.

Thus, there is a continuing need for a better ultrasonic holographyimaging system and especially one which strongly dampens noise.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide an ultrasonic holography imaging system which overcomes theabove noted deficiencies and satisfies the above noted wants.

It is a further object of this invention to provide an ultrasonicholography imaging system that makes it possible to reconstruct a higherquality optical image of the original, ultrasonically illuminatedobject, in real time.

It is a further object of this invention to provide an ultrasonicholography imaging member with preferred specific thickness layers ofliquid thereon, the thickness of the liquid layer adjusted so that itwill respond preferentially to an ultrasonic interference pattern havinga wavelength characteristic with the primary interference between theobject modulated and reference ultrasonic beams, thereby providing forthe strong dampening out and rejection of noise wavelengths from othersources. I

It is a still further object of this invention to provide an ultrasonicholography imaging system with an electric field amplitude enhancingtechnique.

It is a still further object of the invention to provide an ultrasonicholography imaging system to eliminate sources of noise and opticaldistortion normally encountered at a liquid surface type ultrasonichologram, thus enabling real time readout to take place.

It is a still further object of this invention to provide an ultrasonicholography imaging system with an optical electric field means ofamplifying the thin liquid surface relief pattern, thereby increasingthe sensitivity of the system.

It is a still further object of this invention to provide an ultrasonicholography imaging system with a new diverging acoustic lens and a newpreferred elastomeric liquid deformation layer.

The foregoing objects and others are accomplished in accordance withthis invention by providing an imaging member comprising a substrate, atleast partially transparent to ultrasonic radiation, with a thin layerof liquid thereon, the layer preferably of a particular preferredthickness, is used for the detection of the interference patternresulting from the interference of two phase correlated beams ofultrasonic energy, one beam typically being a reference beam and theother an object modulated beam. The free surface of the thin liquidlayer is deformed by the interference pattern to form an acoustichologram which may be used to reconstruct an optical image of the objectand may be used in other advantageous ways as described herein. Electricfield techniques to amplify the ultrasonically produced pattern ofdeformation of the free surface of the thin liquid layer; a divergingacoustic lens and a method of making a preferred elastomeric liquidlayer are also described.

The term liquid and the variant forms thereof used herein to define thelayer of this invention which is ultrasonically deformed includes thosesubstances ordinarily thought of as liquids up to and including therelatively viscous liquids of about 10 poises, includes materials whichare often regarded as soft solids and have viscosities in the range ofabout 10 l0" poises (said soft solid materials typically includingthermoplastics such as those used in frost wrinkling described inGunther et al. US. Pat. No. 3,196,011) and also includes a preferredelastomeric class of materials for use herein.

The term elastomer and the variant forms thereof used herein is definedas an amorphous material which exhibits a restoring force in response toa deformation; that is, an amorphous material which deforms under aforce, and, because of volume and surface forces, tends to return to theform it had before the force was ap plied.

Optically but preferably, because of the amplified patterns produced,electric field techniques may be used to bring the thin liquid layer toa very unstable condition such that when the ultrasonic interferencepattern impinges on the thin liquid layer the instability is triggeredby the pattern which results in a significant amplification of the thinliquid layer free surface ultrasonic interference pattern producedrelief pattern.

two beams approaches the condition of being in the plane of the imagingmember. Preferred thicknesses of the liquid layer which givesubstantially improved results over prior art techniques where there isno control over the thickness of the thin liquid layer and thus whichhave no substantial dampening. out of noise and improved enhancement ofthe special frequencies of interest as provided for by the inventionhereof, have been found to prevail for a liquid layer varying inthickness between about l/30 to about 2 times the wavelength of theultrasonic interference pattern in the plane of the thin liquid layer.This high pass filter characteristic of the thin controlled liquidlayers hereof rejects extraneous sources of noise such as seismicvibrations, acoustic streaming, and vibrations from any source thatwould normally cause surface waves and disrupt and detract from theliquid surface deformation pattern produced by the interference pattern.Coherent or partially coherent light may be reflected from the distortedliquid surface, the ultrasonically distorted surface acting like anultrasonic hologram and reconstructed optical images will appear inspace. These reconstructed optical images may be conveniently viewed bysuitable optical techniques known to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention as well as other objects and further features thereof,reference is made to the following detailed disclosure of this inventiontaken in conjunction with the accompanying drawings wherein:

FIGS. 1 and 2 are partially schematic side views of two embodiments ofthe imaging member according to the invention.

FIGS. 3-6 are other partially schematic illustrations of otherembodiments of imaging members according to the invention with attendantapparatus to place an electric field adjacent or across the liquid layer14 to thereby obtain amplification of the ultrasonically induced surfacedeformation.

FIG. 7 illustrates an example of a preferred mode of ultrasonicallyforming a surface deformation hologram on an imaging member according tothe invention and then optically reconstructing an optical image of theoriginal object; and FIG. 8 shows a cross-section of a preferreddiverging acoustic lens-transducer combination.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 thereis shown imaging member 10 comprising substrate 12 which is at leastpartially transparent to the ultrasonic waves to be used in imaging andliquid layer 14.

For the ultrasonic waves found to be suitable for use herein which aretypically between about 100,000 cycles/second to about 100 megacycles(mc); typical at least partially transparent substrates 12 for waves inthis wavelength region include plastics. A distinct advantage has beenfound in the use of most plastics as substrates 12 in their attenuationproperties. Their thickness and attenuation can be so adjusted so thatthey are sufficiently acoustically transparent yet multiple reflectionswithin the substrate that could give rise to serious defects areeffectively eliminated. The attennation is exponential with distance.For a given attenuating material the thickness is so adjusted that theintensity of a multiply reflected beam emerging from the window is lessthan about 2 percent of the intensity of a directly transmitted beam.Sufficiently attenuating plastics can be found such that the round tripattenuation of a convenient thickness of the plastic will attenu ate amultiply reflected beam to a value much less than that of the directlytransmitted beam. Other materials such as glass and metals may also beused as substrate 12, but most plastics are preferred over glass andmetals since plastics have higher acoustic attenuation. Plasticsubstrates are also preferred in that their acoustic impedance andacoustic velocity are more clearly similar to that of the propagatingliquid and the preferred layers 14, thus reflecting smaller portion ofthe ultrasonic energy entering the substrate allowing for a greaterangle between the reference beam and the object modulated beam andallowing more energy to enter layer 14. It has been found that atsufficiently large angles between the two beams, the maximum angledetermined by the acoustic velocity ratio between the substrate 12 andthe medium of thin liquid layer 14, critical angle reflection takesplace such that no ultrasonic energy can enter the substrate.

While a high density polyethylene substrate 12 gives good results aneven more preferred substrate comprises an acrylic plastic to which athin layer of Teflon has been bonded on both sides to give a total layer12 thickness of about one-half inch.

Layer 14 may preferably comprise water which has low ultrasonicattenuation, is compatible with most materials and is readily available;or oils such as silicone oils which desirably have low vapor pressures,are not easily contaminated, have low surface tensions and a range ofavailable viscosities so that one can adjust the response time of theliquid layer for various surface excitation wavelengths. Dow CorningSilicone Oil No. 704 has been found very effective in this regard.However, any suitable electrically conductive or insulating liquid maybe used.

The preferred class of elastomeric soft solid materials for use hereinincludes both natural, such as natural rubbers, and synthetic polymerswhich have rubberlike characteristics, i.e., are elastic and includingmaterials such as styrene-butadiene, poly-butadiene, neoprene, butyl,polyisoprene, nitrile, and ethylenepropylene rubbers. Preferredelastomers for use herein include water based gelatin gels anddimethylpolysiloxane based silicone gels.

Preferably the liquid layer 14 contains a colorant such as a dye or apigment to prevent multiple reflections of the optical readout beamwithin the volume of the liquid. Such reflections give rise to annoyinginterference patterns.

Referring now to FIG. 2, there is shown a member 10 with an airinterspace '16 above which is an optically transparent window 18.

While window 18 is not necessary for the practice of the inventionhereof, its presence is preferred because one of its main functions isto keep out dust, which especially in the electric field amplifyingtechniques hereof, wherein dust is attracted at an increased rate, isfound to be a problem which may hinder image quality.

Referring now to FIG. 3, there is shown an optional embodiment of animaging member wherein the basic imaging member embodiment is modifiedby including on the substrate 12 a separate electrically conductivelayer 13 of at least partially ultrasonically transparent material suchas a vacuum deposited layer of metal. This embodiment is convenientlyused when corona charging electric field amplification of theultrasonically induced surface deformation of layer 14 is desired. Themember is used in connection with corona discharge device illustrativelytraveling from left to right, depositing illustratively positivelycharged corona, intended to represent any suitable corona dischargedevice. In particular, devices of the general description and generallyoperated as disclosed in Vyverberg US. Pat. No. 2,836,725 and Walkup US.Pat. No. 2,777,957 have been found to be sources of corona useful incorona charging. The device should be placed in such a way that it willcause minimal interference with light entering from the top and used inreconstructing an optical image. Another preferred charging mode whichcauses a minimal interference with reconstruction light is the apparatusand method shown in FIG. 3 of Gunther et al. US. Pat. No. 3,196,011 andthe written portions of the specification relating to FIG. 3. Coronacharging layer 14 to create a surface potential thereon creates asurface instability which is found to amplify the ultrasonically producesurface relief of layer 14. An electrically insulating liquid 14 shouldbe used in this corona charging technique of electric fieldamplification since the layer 14 should support the charge long enoughfor ultrasonic imaging to take place. Liquids with resistivities ofabout 10 or 10 ohm-cm or higher support charge for about 1 to 10 secondsor longer, respectively, and are thus preferred in this regard. It willbe appreciated that conductive layer 13 or even a conductive substrate12 is not necessary in the corona charging electric field amplificationmode hereof since double sided corona charging may be used to chargeinsulating members where two corona charging devices one on each side ofthe imaging member are oppositely charged are traversed in registerrelative to the member. Also if substrate 12 is insulating and no layer13 is used, substrate 12 may be placed in contact with a conductivemember during charging.

Referring now to FIG. 4A there is shown another embodiment of an imagingmember hereof with an electric field means. A liquid electrode layer 24resides on the top surface of layer 14 which is on electrode 13. Liquid24 is electrically conductive, typically immiscible with the material oflayer 14, and may be transparent or reflective to reconstruction lightentering through window I8. Layer 24 may be a thin layer of mercury or agallium-indium alloy or an aqueous salt solution which is in directelectrical contact through wire 26 with power source 28. Preferablyliquid 24 is of a highly reflective metal such as mercury whichincreases the optical efficiency of the system by a factor of about 10over layers 14 such as silicone oil or water with no re fleeting layer24. In this embodiment of FIG. 4A the combined thickness of layers 14and 24 should be between about l/30 to about 2 times the wavelength ofthe ultrasonic interference pattern in the deforming liquid layer.

Referring now to FIG. 48 there is shown another imaging memberembodiment where the entire space be tween optical window 18 and layer14 is filled with a conductive liquid 25.

Window 18 is in intimate contact with the top surface of electricallyconductive liquid 25 which in addition to being optically transparent tolight entering through window 18 serves as an electrode on one side ofthe liquid layer 14 to create an electric field across the thin liquidlayer 14 between electrodes 25 and 13. Conductive frame 19 biases liquid25.

In the electrical field amplification means hereof as shown in FIGS. 3-4where layer 14 is sandwiched between electrodes, potential differencesacross liquid layer 14 in the range of from between about i volts/micronand about 10 volts/micron have been found to be preferred with a minimumthreshold field being about l/lO volt/micron and a maximum practicalfield being about volts/micron. Higher fields than 100 volts/- micronmay be used but arcing and other disruptive forces become a factor.

Referring now to FIG. 5, there is shown another elec tric fieldamplification means wherein a strong bias is applied to electrode 13,which supports liquid layer 14. It has been observed that when arelatively high bias in the order of between about 100 and about 20,000volts is applied to electrode 13, the thin overlayer 14 of deformingliquid will become unstable due to polarization forces created withinthe volume. Then the surface of the liquid will want to deform in thepattern of a distribution of small ultrasonic forces. Electrode 15 isoptional in this embodiment but may be opposite to (and typically equalto) the bias on electrode 13 in order to enhance the electric field.

FIG. 6 is a variation of FIG. 5 wherein the biased transparent electrode28 is maintained near but spaced apart from the liquid layer 14. Withthis configuration biases of about 50 to about 10,000 volts arepreferred to make the liquid surface unstable for amplification, withthe gap between the electrode and the liquid layer preferably beinggreater than the vertical rise of the deformations on layer 14 and lessthan about 1 inch. Electrode 28 may be tin oxide coated glass availableunder the trademark NESA from Pittsburg Plate Glass Company on the underside of transparent window 18.

Referring no to FIG. 7 there is shown the impinging ultrasonic beams 38and 40, traveling through propagating medium 30 typically water. Alsoshown are impinging member 10 hereof and an optical readout system 32.Transducers 34 and 36, connected to the same RF generator 35 emit phasecorrelated beams of ultrasonic energy 38 and 40, respectively, beam 38being the reference beam and beam 40 being the beam modulated byunderwater object 42. Transducers 34 and 36 typically use piezo-electriccrystals such as quartz of piezo ceramic available from Valpey Corp. toproduce narrow pencils of ultrasonic energy. These narrow beams ofultrasonic energy may be diverged by acoustic lenses 44 and 45 which aretypically composed of carbon tetrachloride filled chambers havingspherical exit windows typically made of Mylar polyester from DuPont orother resistant plastic material. Alternatively the ultrasonictransducers may be composed of spherically ground quartz or otherpiezo-electric materials that themselves emit spherical beams ofultrasound.

Alternatively the combination diverging acoustic lens-transducer 59shown in FIG. 8 may be used. 60 is the crystal seated in a crystal mount62 preferably of Teflon tetrafluoroethylene fluorocarbon from DuPont. 64is the frame for example of brass with pressure flanges 66 holding aflexible film window 65 at least a partially ultrasonically transparentmaterial compatible with the propagating medium within which article 59is typically located and the liquid within space 68 defined by the frameportions 70 on each side, the crystal on the bottom and the flexiblefilm window on the top. The liquid within space 68 should have anacoustic velocity less than the propagating medium and be compatiblewith the flexible film window. With water as the propagating medium, aMylar polyethylene terephthalate polyester film about 4 mils thick aswindow 65 and carbon tetrachloride (CCl,,) as the liquid for space 68were found to give good results. Preferred article 59 provides thedesirable result that the transducer itself is the back surface of thelens. It will be appreciated that the flexible window 65 may be convexas well as concave as shown.

Whatever transducer arrangement is chose, these transducers typicallyoperate from a common radio frequency generator 35 which has a long termfrequency stability to ensure mutual coherency of beams 38 and 40 withone another so that they can interact to form a stationary ultrasonicinterference pattern. Typically either beam 38 or 40 is transmittedthrough, reflected or by in any other suitable way modulated by anobject 42 and this beam then passes to imaging member 10 where itinterferes and overlaps with reference beam 38 in liquid layer 14 toproduce a region in which the dynamic ultrasonic pressure experiencesmaxima and minima to thereby create a momentum associated withreflection of the ultrasonic beams on a liquid surface 14 which tends tocause a displacement of the liquid 14 surface. This displacement forpractical purposes is substantially immediately (for example in theorder of about a millisecond) caused by the interference between the twobeams giving rise to a time independent real pattern which may beamplified by the electric field techniques already described and thenreconstructed by coherent or partially coherent light, for example fromlaser light source 50. The light is filtered by pinhole 52, and frommirror 53 passes to parabolic mirror 54 or a lens which may serve as anequivalent where it is commonly but not necessarily collimated whereuponthe rays then pass to ultrasonically deformed liquid surface 14whereupon the rays are reflected from this surface back to mirror 54,being phase modulated, the phase modulated rays normally made convergingconveniently by the same mirror 54, this reflected beam containing atleast two angularly separated images of the acoustically illuminatedobject. One of these may be selected for examination by the telescope56, the other may impinge on, for example, photographic film forrecording.

The following Examples further specifically define the presentultrasonic holography imaging system. The

. parts and percentages are by weight unless otherwise indicated. TheExamples below are intended to illustrate various preferred embodimentsof the ultrasonic holography imaging system of this invention.

EXAMPLE 1 Referring now to FIG. 7, a Teflon coated acrylic plasticsubstrate 12 about one-half inch thick is overcoated with anapproximately 0.1 mm thick layer of dyed water. The layer is exposed toabout 7 me ultrasonic energy as follows:

A first beam 38 is directed towards substrate 12 from the undersideoflayer 12 at an angle of about 12 to imaging member 10 normal. Theobject modulates the beam from transducer 36 and lens 45, sound fromthis source passing through or by the center of the object andintersects the layer 14 making an angle of about 12 degrees to themember 10 normal. These two beams overlap in the thin layer 14 regiongiving rise to interference surfaces that are about 0.5 mm apart.

Imaging member 10 is exposed continuously to these ultrasonic beams togive a constant relief pattern to the surface of layer 14.

The hologram surface of layer 14 is reconstructed by directing lightfrom a continuous wave laser of about 10 milliwatt optical power so thatthe laser light hits the top surface of layer 14 at normal incidence. A3-D image of the acoustically illuminated object is then seen by a humanobserver using the telescope.

EXAMPLE Il Example I is followed except that liquid layer 14 is a dyedelastomer dimethylpolysiloxane silicone gel made by combining about 1part of Dow Corning No. 182, silicone resin potting compound andanywhere from about 0 to about 30 parts of oil, Dow Corning No. 200dimethylpolysiloxane silicone and heating between about 50C. and aboutC. for between about 15 minutes to about 24 hours.

Contigous" as used herein is defined as in Websters New CollegiateDictionary, second edition, 1960; In actual contact; touching; also,near, though not in contact; adjoining."

Although specific components and proportions have been stated in theabove description of preferred embodiments of the ultrasonic holographicimaging system hereof, other suitable materials as listed herein may beused with similar results. In addition other materials which existpresently or may be discovered may be used or added to the mixture andvariations may be made in the various processing steps to synergize,enhance and otherwise modify its properties. For example, separateelectrode layers 13 and 28 are unnecessary if layers 12 and 18,respectively, are themselves electrically conductive. Also, it will beappreciated that since sound waves pass through many substances, one ofthe promising applications hereof is in X-ray type work.

It will be understood that various other changes in the details,materials, steps and arrangements of parts which have been hereindescribed and illustrated in order to explain the nature of theinvention will occur to and may be made by those skilled in the art upona reading of this disclosure, such changes are intended to be includedwithin the principle and scope of this invention.

What is claimed is:

1. An ultrasonic holography imaging method comprising the steps of a.providing an imaging member comprising a substrate at least partiallytransparent to ultrasonic radiation with a deformable substantiallysmooth surface solid elastomer layer thereon;

b. directing an object modulated coherent ultrasonic beam at saidmember; and

c. directing a coherent reference beam of ultrasonic radiation phasecorrelated with the coherent radia tion of said object modulatedultrasonic beam at said member wherein both the object modulated beamand reference beam are directed to said deformable solid elastomer layerthrough said substrate to create a stationary ultrasonic interferencepattern in said deformable solid elastomer layer to thereby create anultrasonic hologram in the form of surface ripples on said deformablesolid elastomer layer.

2. An imaging method according to claim 1 wherein, before imaging, thethickness of said deformable solid elastomer layer is between about 1/30to about 2 times the wavelength of the ultrasonic interference patternformed in the plane of said layer by steps (b) and (c) of claim 1.

3. An imaging method according to claim 2 wherein said elastomercomprises a material selected from the group consisting of water basedgels and dimethylpolysiloxane based silicone gels.

4. An imaging method according to claim 2 wherein steps (b) and (c) ofclaim 1 are repeated at least once after allowing the elastomer to snapback to its original substantially smooth surface condition after theprevious ultrasonic imaging.

5. An imaging method according to claim 1 wherein said substratecomprises a plastic layer with at least one outer surface layerprotecting said plastic layer from any degrading effect from either thepropagating medium for said ultrasonic beams or the deformable solidelastomer layer.

6. An imaging method according to claim 1 including directing areconstructing light to said deformable solid elastomer layer upon whichhas been formed a hologram in the form of surface ripples wherein saiddeformable solid elastomer layer contains a colorant to prevent multiplereflections of the reconstructing light within the volume of saiddeformable solid elastomer layer.

7. An ultrasonic holography imaging method comprising the steps of:

a. providing an imaging member comprising a substrate at least partiallytransparent to ultrasonic radiation with a deformable substantiallysmooth surface solid elastomer layer thereon;

b. directing an object modulated coherent ultrasonic beam at saidmember; and

c. directing a coherent reference beam of ultrasonic radiation phasecorrelated with the coherent radiation of said object modulatedultrasonic beam at said member to create a stationary ultrasonicinterference pattern in said solid elastomer layer to thereby create anultrasonic hologram in the form of surface ripples on said solidelastomer layer.

8. An imaging method according to claim 7 wherein both said objectmodulated and said reference beams are propagated through water to saidimaging member, both means impinging upon the imaging member from thesubstrate side.

9. An imaging method according to claim 7 wherein said substratesubstantially dampens multiple acoustic reflections within thesubstrate.

10. An imaging method according to claim 7 including directing areconstructing light to said solid elasto mer layer upon which has beenformed a hologram in the form of surface ripples wherein said solidelastomer layer contains a colorant to prevent multiple reflections ofthe reconstructing light within the volume of said solid elastomerlayer.

1 1. An imaging method according to claim 7 wherein said substratecomprises a plastic layer with at least one outer surface layerprotecting said plastic layer from any degrading effect from either thepropagating medium for said ultrasonic beams or the solid elastomerlayer.

7 12. An imaging method according to claim 9 wherein said substratecomprises a plastic.

13. An acoustic holographic imaging apparatus comprising:

a. a substrate at least partially transparent to acoustic radiation, anda deformable substantially smooth surface solid elastomer layer on saidsubstrate for detecting the interference pattern resulting from theimpingement of the two phase correlated beams of acoustic energy,recited below; and

b. means for directing at least two phase correlated beams of acousticenergy at said deformable solid elastomer layer by directing said beamsthrough said substrate, one beam being a reference beam and the other anobject modulated beam, the thickness of said deformable layer being apredetermined magnitude relative to the wavelength of the interferencepattern impinging on the deformable layer so as to substantially dampenextraneous sources of acoustic noise.

14. Apparatus as set forth in claim 13 wherein said substrate is atleast partially transparent to said two phase correlated beams butsubstantially dampens multiple acoustic reflections within thesubstrate.

15. Apparatus as set forth in claim 13 further including optical readoutmeans comprising a reconstructing light source directed to saiddeformable solid elastomer layer upon which has been formed a hologramin the form of surface ripples in said deformable solid elastomer layerdue to a stationary acoustic interference pat tern caused by saidreference and object modulated beams, and

detection means for detecting the phase modulated beams from saiddeformable solid elastomer layer for optical readout of the hologramformed thereon.

16. Apparatus as set forth in claim 15 wherein said deformable solidelastomer layer contains a colorant to prevent multiple reflections ofthe optical readout beam within the volume of said deformable solidelastomer layer.

17. Apparatus as set forth in claim 15 wherein said solid elastomercomprises a material selected from the group consisting of water basedgels and dimethylpolysiloxane based silicone gels.

18. Apparatus as set forth in claim 14 wherein said substrate comprisesa plastic.

19. Apparatus as set forth in claim 18 wherein said plastic comprises amaterial selected from the group consisting of polyethylene andacrylics.

20. Apparatus as set forth in claim 19 wherein said plastic layer has atleast one outer surface of tetrafluoroethylene fluorocarbon.

21. Apparatus as set forth in claim 14 wherein the intensity of anymultiply reflected beam emerging from the substrate to the deformablesolid elastomer layer is less than about 2 percent of the intensity of adirectly transmitted beam.

22. An ultrasonic holography imaging method comprising the steps of:

a. providing an imaging member comprising a substrate at least partiallytransparent to ultrasonic radiation with a deformable liquid layerthereon;

b. directing an object modulated coherent ultrasonic beam at saidmember;

c. directing a coherent reference beam of ultrasonic radiation phasecorrelated with the coherent radiation of said object modulatedultrasonic beam at said member to create a stationary ultrasonicinterference pattern in said deformable liquid layer; and

d. applying an electric field to said deformable liquid layer so thatsaid electric field is present at least during part of steps (b) and (c)to thereby create an amplified ultrasonic hologram in the form ofsurface ripples on said deformable liquid layer.

23. An imaging method according to claim 22 wherein said field isapplied by electrostatically charging the free surface of anelectrically insulating deformable liquid layer.

24. An imaging method according to claim 23 wherein the electric fieldestablished across the deformable liquid layer is in the range of frombetween about 1 volt/micron to about volts/micron.

25. An imaging method according to claim 22 wherein an electrode ispositioned contiguous the deformable liquid layer, the electrode at abias between about 100 and 20,000 volts.

26. An imaging method according to claim 25 wherein the electrode is notspaced from the deformable liquid layer by a distance of more than about1 inch.

27. An imaging method according to claim 25 is a thin overlayer ofelectrically conductive liquid overlying said deformable liquid layer.

28. An imaging method according to claim 22 wherein said deformableliquid layer is an elastomer.

29. An imaging method according to claim 28 wherein, before imaging,said elastomer layer has a substantially smooth surface.

30. An imaging method according to claim 28 wherein said elastomercomprises a material selected from the group consisting of water basedgels and-dimethylpolysiloxane based silicone gels.

31. An imaging method according to claim 28 wherein steps (b) and (c) ofclaim 22 are repeated at least once after allowing the elastomer to snapback to its original substantially smooth surface condition after aprevious ultrasonic imaging.

32. An imaging method according to claim 22 wherein said substratesubstantially dampens multiple acoustic reflections within thesubstrate.

33. An imaging method according to claim 22 wherein said substratecomprises a plastic layer with at least one outer surface layerprotecting said plastic layer from any degrading effect from either thepropagating medium for said ultrasonic beams or the deformable liquidlayer.

34. An imaging method according to claim 22 including directing areconstructing light to said deformable liquid layer upon which had beenformed a hologram in the form of surface ripples wherein said deformableliquid layer contains a colorant to prevent multiple reflections of thereconstructing light within the volume of said deformable liquid layer.

35. An imaging method according to ,claim 22 wherein said reconstructinglight is directed through an at least partially transparent windowbefore it reaches said deformable liquid layer, the window to protectsaid deformable liquid layer from external foreign material.

36. An imaging method according to claim 24 wherein said deformableliquid layer has a bulk electrical resistivity greater than about l0ohm-cm.

37. An imaging method according to claim 22 wherein at least a portionof said electric field is applied between an electrically conductivelayer on the top surface of said deformable liquid layer and anothersource of potential or ground on the opposite side of said deformableliquid layer from said electrically conductive layer.

38. An imaging method according to claim 37 wherein said electricallyconductive layer is immiscible with the material of the deformableliquid layer and capable of deforming in accordance with andcorresponding to the deformations in said deformable liquid layer andwherein the combined thickness of said electrically conductive layer andsaid deformable liquid layer is between about 1/30 to about 2 times thewavelength of the. ultrasonic interference pattern to be produced in thedeformable liquid layer.

39. An imaging method according to claim 38 wherein said electricallyconductive layer comprises a reflective metal.

40. An imaging method according to claim 38 wherein said electricallyconductive layer is a liquid.

41. An imaging method according to claim 35 wherein the space betweensaid window and the top surface of said deformable layer is filled withan electrically conductive liquid.

42. An imaging method according to claim 41 wherein the electrical fieldis applied between said electrically conductive liquid and a potentialsource or ground on the opposite side of said deformable liquid layerfrom said electrically conductive layer.

43. An imaging method according to claim 22 wherein the electric fieldestablished across the deformable liquid layer is in the range of frombetween about l/l0 volt/micron to about volts/micron.

44. An imaging method according to claim 22 wherein said deformableliquid layer rests on an electrically conductive layer biased to apotential within the range of between about 100 volts and about 20,000volts.

45. An imaging method according to claim 32 wherein said substratecomprises a plastic.

46. An acoustic holographic imaging apparatus comprising:

a. a substrate at least partially transparent to acoustic radiation, anda deformable layer on said substrate for detecting the interferencepattern resulting from the impingement of the two phase correlated beamsof acoustic energy recited below;

b. means for directing at least two phase correlated beams of acousticenergy at said deformable layer, one beam being a reference beam and theother an object modulated beam, the thickness of said deformable layerbeing a predetermined magnitude relative to the wavelength of theinterference pattern impinging on the deformable layer so as tosubstantially dampen extraneous sources of acoustic noise; and

c. means for applying an electric field to said deformable layer toamplify the acoustic hologram formed as surface ripples on saiddeformable layer.

47. Apparatus as set forth in claim 46 wherein said electric fieldapplying means comprises a corona discharge apparatus.

48. Apparatus as set forth in claim 46 wherein said electric fieldapplying means comprises an electrically conductive liquid layer on thetop surface of said detecting layer.

49. Apparatus as set forth in claim 48 further including an electricallyconductive layer at least partially transparent to acoustic radiationand positioned between said deformable layer and said substrate.

50. Apparatus as set forth in claim 48 wherein said substrate iselectrically conductive.

51. Apparatus as set forth in claim 48 further including a potentialsource coupled to said conductive liquid layer for applying saidelectric field to said deformable layer.

52. Apparatus as set forth in claim 51 further including a framesupporting said substrate with an optically transparent window toprovide enclosed chamber including said deformable layer and saidconductive layer.

53. Apparatus as set forth in claim 52 wherein said frame is insulatingand said potential source is external to and is applied through saidframe to bias said conductive layer.

54. Apparatus as set forth in claim 52 wherein said frame is conductiveand said potential source is external to and is coupled to said frame tobias the conductive layer on said deformable layer.

55. Apparatus as set forth in claim 54 wherein said conductive layer onsaid deformable layer occupies the entire space of the chamber formed bythe frame and optically transparent window.

56. Apparatus as set forth in claim 52 wherein said conductive layerover said deformable layer occupies the space formed by said frame andsaid optically transparent window, and further including an electricallyconducting electrode on the inner surface of said optically transparentwindow wherein said potential source is coupled to said conductive layerto provide said electric field.

57. Apparatus according to claim 46 wherein the intensity of anymultiply reflected beam emerging from the substrate to the deformablelayer is less than about 2 percent of the intensity of a directlytransmitted beam.

58. An acoustic holographic imaging apparatus comprising:

a substrate at least partially transparent to acoustic radiation, and adeformable layer on said substrate for detecting the interferencepattern resulting from the impingement of the two phase correlated beamsof acoustic energy recited below;

means for directing at least two phase correlated beams of acousticenergy at said deformable layer, one beam being a reference beam and theother an object modulated beam, the thickness of said deformable layerbeing a predetermined magnitude relative to the wavelength of theinterference pattern impinging on the deformable layer so as tosubstantially dampen extraneous sources of acoustic noise;

optical readout means comprising a reconstructing light source directedto said deformable layer upon which has been formed a hologram in theform of surface ripples in said deformable layer due to a stationaryacoustic interference pattern caused by said reference and objectmodulated beams;

detection means for detecting the phase modulated beams from saiddeformable layer surface for optical readout of the hologram formedthereon; and

means for applying an electric field to said deformable layer to createan amplified acoustic hologram in the form of said surface ripples onsaid deformable layer.

59. Apparatus according to claim 58 wherein the intensity of anymultiply reflected beam emerging from the substrate to the deformablelayer is less than about 2 percent of the intensity of a directlytransmitted beam.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo.3,742,439 Dated June 26, 1973 Inventor(s) Nicholas K. Sheridon It iscertified that error appears in theabove-identified patent and that saidLetters Patent are hereby corrected as shown below:

Column 2, lines 14-15, "optical" should read optional--. Column 2, line-"59 "optically" should read -optionally---. Column 6, line 49, "no"should read --now-.

Column 6, lines 5 1-52, "impinging" should read imaging--. Column 6,line 1 58, "of" should read --or- I Column 7, line 2 5, "chose" shouldread chosen-- Claim 8, line 4,. "means" should read beams-- Signed andsealed this 20th day of August 1974.

(SEAL) Attest:

MCCOY M. GIBSONI,,"JR. c. MARSHALL DANN Attesting Officer Commissionerof Patents FORM PC4050 "$59) uscoMM-Dc 60376-P69 I' 9 U.S GOVERNMENTPRINTING OFFICE 1559 0-365-334,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,7Dated June 26, 1973 Inventor(s) Nicholas K. Sheridon It is certifiedthat error appears in theabove-identified patent and that said LettersPatent are hereby corrected as shown-below:

Column 2, lines 14-15, "optical" should read -,optional. Column 2, line-59, "optically" should read --opti onally--. Column 6, line 49 "noshould read -now---. I

Column 6, lines 51-52, "impinging" should read --imaging--. Column 6,line-F58, "of" should read -or-- I Column 7, line 25, "chose" shouldread ---chos en--.

Claim 8, line 4-, "means" should read --beams-- Signed and sealed this20th day of August 1974.

(SEAL) Attest: McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting OfficerCommissioner of Patents FORM PO-105O (IO-69) u5 c 50 7 9 9 I. w U.5.GOVERNMENT PRINTING OFFICE: I969 0-356-334,

2. An imaging method according to claim 1 wherein, before imaging, thethickness of said deformable solid elastomer layer is between about 1/30to about 2 times the wavelength of the ultrasonic interference patternformed in the plane of said layer by steps (b) and (c) of claim
 1. 3. Animaging method according to claim 2 wherein said elastomer comprises amaterial selected from the group consisting of water based gels anddimethylpolysiloxane based silicone gels.
 4. An imaging method accordingto claim 2 wherein steps (b) and (c) of claim 1 are repeated at leastonce after allowing the elastomer to snap back to its originalsubstantially smooth surface condition after the previous ultrasonicimaging.
 5. An imaging method according to claim 1 wherein saidsubstrate comprises a plastic layer with at least one outer surfacelayer protecting said plastic layer from any degrading effect fromeither the propagating medium for said ultrasonic beams or thedeformable solid elastomer layer.
 6. An imaging method according toclaim 1 including directing a reconstructing light to said deformablesolid elastomer layer upon which has been formed a hologram in the formof surface ripples wherein said deformable solid elastomer layercontains a colorant to prevent multiple reflections of thereconstructing light within the volume of said deformable solidelastomer layer.
 7. An ultrasonic holography imaging method comprisingthe steps of: a. providing an imaging member comprising a substrate atleast partially transparent to ultrasonic radiation with a deformablesubstantially smooth surface solid elastomer layer thereon; b. directingan object modulated coherent ultrasonic beam at said member; and c.directing a coherent reference beam of ultrasonic radiation phasecorrelated with the coherent radiation of said object modulatedultrasonic beam at said member to create a stationary ultrasonicinterference pattern in said solid elastomer layer to thereby create anultrasonic hologram in the form of surface ripples on said solidelastomer layer.
 8. An imaging method according to claim 7 wherein bothsaid object modulated and said reference beams are propagated throughwater to said imaging member, both means impinging upon the imagingmember from the substrate side.
 9. An imaging method according to claim7 wherein said substrate substantially dampens multiple acousticreflections within the substrate.
 10. An imaging method according toclaim 7 including directing a reconstructing light to said solidelastomer layer upon which has been formed a hologram in the form ofsurface ripples wherein said solid elastomer layer contaIns a colorantto prevent multiple reflections of the reconstructing light within thevolume of said solid elastomer layer.
 11. An imaging method according toclaim 7 wherein said substrate comprises a plastic layer with at leastone outer surface layer protecting said plastic layer from any degradingeffect from either the propagating medium for said ultrasonic beams orthe solid elastomer layer.
 12. An imaging method according to claim 9wherein said substrate comprises a plastic.
 13. An acoustic holographicimaging apparatus comprising: a. a substrate at least partiallytransparent to acoustic radiation, and a deformable substantially smoothsurface solid elastomer layer on said substrate for detecting theinterference pattern resulting from the impingement of the two phasecorrelated beams of acoustic energy, recited below; and b. means fordirecting at least two phase correlated beams of acoustic energy at saiddeformable solid elastomer layer by directing said beams through saidsubstrate, one beam being a reference beam and the other an objectmodulated beam, the thickness of said deformable layer being apredetermined magnitude relative to the wavelength of the interferencepattern impinging on the deformable layer so as to substantially dampenextraneous sources of acoustic noise.
 14. Apparatus as set forth inclaim 13 wherein said substrate is at least partially transparent tosaid two phase correlated beams but substantially dampens multipleacoustic reflections within the substrate.
 15. Apparatus as set forth inclaim 13 further including optical readout means comprising areconstructing light source directed to said deformable solid elastomerlayer upon which has been formed a hologram in the form of surfaceripples in said deformable solid elastomer layer due to a stationaryacoustic interference pattern caused by said reference and objectmodulated beams, and detection means for detecting the phase modulatedbeams from said deformable solid elastomer layer for optical readout ofthe hologram formed thereon.
 16. Apparatus as set forth in claim 15wherein said deformable solid elastomer layer contains a colorant toprevent multiple reflections of the optical readout beam within thevolume of said deformable solid elastomer layer.
 17. Apparatus as setforth in claim 15 wherein said solid elastomer comprises a materialselected from the group consisting of water based gels anddimethylpolysiloxane based silicone gels.
 18. Apparatus as set forth inclaim 14 wherein said substrate comprises a plastic.
 19. Apparatus asset forth in claim 18 wherein said plastic comprises a material selectedfrom the group consisting of polyethylene and acrylics.
 20. Apparatus asset forth in claim 19 wherein said plastic layer has at least one outersurface of tetrafluoroethylene fluorocarbon.
 21. Apparatus as set forthin claim 14 wherein the intensity of any multiply reflected beamemerging from the substrate to the deformable solid elastomer layer isless than about 2 percent of the intensity of a directly transmittedbeam.
 22. An ultrasonic holography imaging method comprising the stepsof: a. providing an imaging member comprising a substrate at leastpartially transparent to ultrasonic radiation with a deformable liquidlayer thereon; b. directing an object modulated coherent ultrasonic beamat said member; c. directing a coherent reference beam of ultrasonicradiation phase correlated with the coherent radiation of said objectmodulated ultrasonic beam at said member to create a stationaryultrasonic interference pattern in said deformable liquid layer; and d.applying an electric field to said deformable liquid layer so that saidelectric field is present at least during part of steps (b) and (c) tothereby create an amplified ultrasonic hologram in the form of surfaceripples on said deformable liquid layer.
 23. An imaging method accordingto claim 22 wherein said field is applied by electrostatiCally chargingthe free surface of an electrically insulating deformable liquid layer.24. An imaging method according to claim 23 wherein the electric fieldestablished across the deformable liquid layer is in the range of frombetween about 1 volt/micron to about 10 volts/micron.
 25. An imagingmethod according to claim 22 wherein an electrode is positionedcontiguous the deformable liquid layer, the electrode at a bias betweenabout 100 and 20,000 volts.
 26. An imaging method according to claim 25wherein the electrode is not spaced from the deformable liquid layer bya distance of more than about 1 inch.
 27. An imaging method according toclaim 25 is a thin overlayer of electrically conductive liquid overlyingsaid deformable liquid layer.
 28. An imaging method according to claim22 wherein said deformable liquid layer is an elastomer.
 29. An imagingmethod according to claim 28 wherein, before imaging, said elastomerlayer has a substantially smooth surface.
 30. An imaging methodaccording to claim 28 wherein said elastomer comprises a materialselected from the group consisting of water based gels anddimethylpolysiloxane based silicone gels.
 31. An imaging methodaccording to claim 28 wherein steps (b) and (c) of claim 22 are repeatedat least once after allowing the elastomer to snap back to its originalsubstantially smooth surface condition after a previous ultrasonicimaging.
 32. An imaging method according to claim 22 wherein saidsubstrate substantially dampens multiple acoustic reflections within thesubstrate.
 33. An imaging method according to claim 22 wherein saidsubstrate comprises a plastic layer with at least one outer surfacelayer protecting said plastic layer from any degrading effect fromeither the propagating medium for said ultrasonic beams or thedeformable liquid layer.
 34. An imaging method according to claim 22including directing a reconstructing light to said deformable liquidlayer upon which had been formed a hologram in the form of surfaceripples wherein said deformable liquid layer contains a colorant toprevent multiple reflections of the reconstructing light within thevolume of said deformable liquid layer.
 35. An imaging method accordingto claim 22 wherein said reconstructing light is directed through an atleast partially transparent window before it reaches said deformableliquid layer, the window to protect said deformable liquid layer fromexternal foreign material.
 36. An imaging method according to claim 24wherein said deformable liquid layer has a bulk electrical resistivitygreater than about 1013 ohm-cm.
 37. An imaging method according to claim22 wherein at least a portion of said electric field is applied betweenan electrically conductive layer on the top surface of said deformableliquid layer and another source of potential or ground on the oppositeside of said deformable liquid layer from said electrically conductivelayer.
 38. An imaging method according to claim 37 wherein saidelectrically conductive layer is immiscible with the material of thedeformable liquid layer and capable of deforming in accordance with andcorresponding to the deformations in said deformable liquid layer andwherein the combined thickness of said electrically conductive layer andsaid deformable liquid layer is between about 1/30 to about 2 times thewavelength of the ultrasonic interference pattern to be produced in thedeformable liquid layer.
 39. An imaging method according to claim 38wherein said electrically conductive layer comprises a reflective metal.40. An imaging method according to claim 38 wherein said electricallyconductive layer is a liquid.
 41. An imaging method according to claim35 wherein the space between said window and the top surface of saiddeformable layer is filled with an electrically conductive liquid. 42.An imaging method according to claim 41 wherein the electrical field isapplied between Said electrically conductive liquid and a potentialsource or ground on the opposite side of said deformable liquid layerfrom said electrically conductive layer.
 43. An imaging method accordingto claim 22 wherein the electric field established across the deformableliquid layer is in the range of from between about 1/10 volt/micron toabout 100 volts/micron.
 44. An imaging method according to claim 22wherein said deformable liquid layer rests on an electrically conductivelayer biased to a potential within the range of between about 100 voltsand about 20,000 volts.
 45. An imaging method according to claim 32wherein said substrate comprises a plastic.
 46. An acoustic holographicimaging apparatus comprising: a. a substrate at least partiallytransparent to acoustic radiation, and a deformable layer on saidsubstrate for detecting the interference pattern resulting from theimpingement of the two phase correlated beams of acoustic energy recitedbelow; b. means for directing at least two phase correlated beams ofacoustic energy at said deformable layer, one beam being a referencebeam and the other an object modulated beam, the thickness of saiddeformable layer being a predetermined magnitude relative to thewavelength of the interference pattern impinging on the deformable layerso as to substantially dampen extraneous sources of acoustic noise; andc. means for applying an electric field to said deformable layer toamplify the acoustic hologram formed as surface ripples on saiddeformable layer.
 47. Apparatus as set forth in claim 46 wherein saidelectric field applying means comprises a corona discharge apparatus.48. Apparatus as set forth in claim 46 wherein said electric fieldapplying means comprises an electrically conductive liquid layer on thetop surface of said detecting layer.
 49. Apparatus as set forth in claim48 further including an electrically conductive layer at least partiallytransparent to acoustic radiation and positioned between said deformablelayer and said substrate.
 50. Apparatus as set forth in claim 48 whereinsaid substrate is electrically conductive.
 51. Apparatus as set forth inclaim 48 further including a potential source coupled to said conductiveliquid layer for applying said electric field to said deformable layer.52. Apparatus as set forth in claim 51 further including a framesupporting said substrate with an optically transparent window toprovide enclosed chamber including said deformable layer and saidconductive layer.
 53. Apparatus as set forth in claim 52 wherein saidframe is insulating and said potential source is external to and isapplied through said frame to bias said conductive layer.
 54. Apparatusas set forth in claim 52 wherein said frame is conductive and saidpotential source is external to and is coupled to said frame to bias theconductive layer on said deformable layer.
 55. Apparatus as set forth inclaim 54 wherein said conductive layer on said deformable layer occupiesthe entire space of the chamber formed by the frame and opticallytransparent window.
 56. Apparatus as set forth in claim 52 wherein saidconductive layer over said deformable layer occupies the space formed bysaid frame and said optically transparent window, and further includingan electrically conducting electrode on the inner surface of saidoptically transparent window wherein said potential source is coupled tosaid conductive layer to provide said electric field.
 57. Apparatusaccording to claim 46 wherein the intensity of any multiply reflectedbeam emerging from the substrate to the deformable layer is less thanabout 2 percent of the intensity of a directly transmitted beam.
 58. Anacoustic holographic imaging apparatus comprising: a substrate at leastpartially transparent to acoustic radiation, and a deformable layer onsaid substrate for detecting the interference pattern resulting from theimpingement of the two phase correlated bEams of acoustic energy recitedbelow; means for directing at least two phase correlated beams ofacoustic energy at said deformable layer, one beam being a referencebeam and the other an object modulated beam, the thickness of saiddeformable layer being a predetermined magnitude relative to thewavelength of the interference pattern impinging on the deformable layerso as to substantially dampen extraneous sources of acoustic noise;optical readout means comprising a reconstructing light source directedto said deformable layer upon which has been formed a hologram in theform of surface ripples in said deformable layer due to a stationaryacoustic interference pattern caused by said reference and objectmodulated beams; detection means for detecting the phase modulated beamsfrom said deformable layer surface for optical readout of the hologramformed thereon; and means for applying an electric field to saiddeformable layer to create an amplified acoustic hologram in the form ofsaid surface ripples on said deformable layer.
 59. Apparatus accordingto claim 58 wherein the intensity of any multiply reflected beamemerging from the substrate to the deformable layer is less than about 2percent of the intensity of a directly transmitted beam.